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Biological Nitrogen Fixation

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Biological Nitrogen Fixation is the process by which some organisms convert atmospheric nitrogen into a usable form of nitrogen. That can be used by plants and other organisms. Biological Nitrogen Fixation is occurred by a diverse no. of microorganisms including plants, animals, bacteria, archaea, and some fungi. Biological nitrogen fixation is an important process in agriculture, as it allows crops to obtain the nitrogen they need for growth without the use of synthetic fertilizers, which can have negative environmental impacts

Nitrogen Fixation

Natural Nitrogen Fixation is a strategy for eliminating nitrogen from the climate. Certain microbes and prokaryotes convert the organic course of nitrogen fixation is the most important phase in the nitrogen cycle. Certain bacterial species form nitrogen from the air into smelling salts. Nitrogen Cycel is of 2 types those are:

  • Abiological Nitrogen Fixation
  • Biological Nitrogen Fixation

Biological Nitrogen Fixation

Biological Nitrogen Fixation is the process by which various groups of microorganisms change the atmospheric nitrogen into the usable form of nitrogen i.e. ammonia. Ammonia is further used by plants and animals to make organic compounds like nucleic acids or proteins. The bacteria responsible for biological nitrogen fixation are called diazotrophs, and they include a variety of species such as Rhizobium, Azotobacter, and Cyanobacteria. 

Diazotrophs form symbiotic relationships with plants, living in nodules on the roots of leguminous plants such as peas, beans, and clover. The bacteria take in atmospheric nitrogen and convert it into ammonia, which is then taken up by the plant and used for growth and development. In non-symbiotic relationships, free-living diazotrophs fix nitrogen in soil or water, making it available to other organisms in the ecosystem.

N2 + 8H+ +8e−→2NH3 + H2

Biological nitrogen fixation is essential for maintaining soil fertility and reducing the need for synthetic fertilizers. Biological Nitrogen Fixation also plays a crucial role in global nitrogen cycling, influencing the amount of nitrogen available to support plant growth and ultimately affecting the productivity of terrestrial and aquatic ecosystems.

Also Read: Types of Ecosystem

Process of Biological Nitrogen Fixation

Biological nitrogen fixation is a process that takes place in 2 stages those are:

Stage 1: Rhizobium contacts a susceptible root hair

Legumes plant’s roots release some chemicals like (amino acids, organic acids, and flavinoids) which attract the rhizobium. Such attraction is known as a chemotactic attraction.

Stage 2: Bacteria invade the root hair

Hairs of root curled because of specific complex polysaccharides present on the rhizobium surface recognized by lectins. The bacteria attached and invade the root cells and divide. For the dedifferentiation of cortical and pericycle cells, PGRs ( are required. Auxin is provided by the root, while bacteria provide cytokinin.

Mechanism of Biological Nitrogen Fixation

Nitrogen Fixation by Nitrogenase Complex


Biological Nitrogen fixation is catalyzed by the enzyme complex known as Nitrogenase Complex. 3 different types of nitrogenase are present depending on the requirement of molybdenum, vanadium, or iron. Nitrogenase contains 2 proteins: Dinitrogenase reductase, and Dinitrogenase. Nitrogen Fixation is a reductive process so they require an electron donor. In most microorganisms, ferredoxin is used as an electron donor. Almost 16 ATP are used to reduce one molecule of N2.

FAQs on Biological Nitrogen Fixation

Q1: How does biological nitrogen fixation occur?


Biological Nitrogen fixation occurs with the help of microorganisms that convert the environment’s nitrogen into a usable form of nitrogen.

Q2: What are 2 types of biological nitrogen fixation?


There are 2 types of biological nitrogen fixation depending on the bacteria:

  • Non-Symbiotic (done by free-living bacteria)
  • Symbiotic Biological Nitrogen Fixation

Q3: Who discovered Biological Nitrogen Fixation?


 German agronomist Hermann Hellriegel discovered biological nitrogen fixation.

Q4: Which enzyme is responsible for biological nitrogen fixation?


Nitrogenase is the enzyme that is responsible for the process of biological nitrogen fixation.

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Last Updated : 28 Apr, 2023
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